Energy Conservation as the Basis of Relativistic Mechanics, II, R. Penrose and W. Rindler, Am. J. Phys. 33, 995-997, 1965
From the relativity principle and the conservation of energy in particle collisions we deduce the form of the energy function, and the conservation of inertial mass and three-momentum. We show that the arguments are parallel under Einsteinian and Galilean kinematics.